The present invention relates generally to internal combustion engines. More specifically, the present invention relates generally valves for internal combustion engines. Still more specifically, the present invention relates to an apparatus and method for testing the structural integrity and wear characteristics of internal combustion engine valves under simulated operating conditions.
Internal combustion engines include exhaust valves that control the intake of an air-fuel mixture and discharge of spent gas from the combustion chamber. Engine valves typically include a valve head connected to a valve stem. The valve stem extends from the valve head. The valve head is received on a seat disposed within the combustion chamber. The valves typically oscillate from a seated position to a lifted or unseated position inside the cylinder head.
Such engine valves are subjected to extreme heat cycles. Specifically, when a truck is climbing a steep hill, the engine is under stress and the valves become very hot, typically in the temperature range of 700 EC to 800 EC. After the truck reaches the top of a hill and proceeds downhill at a restrained speed controlled by the transmission, air flowing over the engine can cool the valve and cylinder at a dramatic pace.
In addition to these extreme heat cycles, the valve is obviously subjected to repetitive collision against the valve seat or seat insert. All of the above factors contribute to valve wear.
It has been observed that valves tend to fail in three distinct modes: radial cracking along the valve face, wear between the valve face and seat and an erosive attack that leads to guttering. Guttering tends to predominate in engines burning diesel fuel while radial cracking tends to predominate in gasoline burning engines where engine temperatures can be higher.
It has been found that guttering in diesel engines results primarily from an oxidation phenomenon along the contact face that is accelerated by the presence of deposits or contaminants. The deposits, which can strongly adhere to the valve contact face, can be formed by the combustion of additives found in the engine oil. An oxidized region of the valve face can be brittle and can erode away prematurely during the repetitive seating and lifting cycle. This guttering phenomenon can accelerate quickly until engine performance is degraded to the point of failure.
The cause of radial cracking appears to be related in part to residual stresses associated with the weld face. Because radial cracking is more common in gasoline burning engines, which typically operate at a higher temperature than diesel engines, radial cracking has been associated with high temperature fatigue of the metal. The cause of valve face to valve seat wear is especially problematic and could be solved using different alloys. However, the use of exotic alloys in manufacturing valves could be cost prohibitive.
To lower warranty costs, the use of more new materials in making valves and valve seats requires that the new materials be tested. Currently, no engine valve wear test apparatus is available which can test engine valves at extreme operating conditions in terms of temperature, pressure, valve rotation and valve offset. The present invention is directed toward overcoming these deficiencies.
The present invention satisfies the aforenoted needs by provided an apparatus for testing engine valves and a method for testing engine valves.
In one aspect of the present invention, a housing is used to simulate a cylinder. The housing has a first end and second end. The first end of the housing has an eccentric bore for receiving a seat fixture. The housing further has an axial passage that extends through the second end of the housing and into the eccentric bore. The seat fixture is replaceable and allows the apparatus to test a variety of valve sizes and configurations. The seat fixture has a first end, a second end and an axial passage extending between the first and second ends. The first end of the seat fixture is supported within the eccentric bore of the housing at the first end of the housing. The axial passage of the seat fixture is wider at the first end of the seat fixture and receives a seat insert or a valve seat at this wider section. The seat insert receives the head of the valve. The stem of the valve extends through the axial passages of the seat fixture and the housing and out the second end of the housing. The seat fixture is rotatable within the eccentric bore of the housing to provide an axial offset between the valve and the axial passage of the housing. In this manner, valves can be tested in an offset position. The valve engages at least one actuator that applies force to the valve in a first axial direction that simulates a lifting of the valve head off of the seat insert. The actuator also applies force to the valve in a second and opposite axial direction that simulates a pressing of the valve onto the seat insert.
In another aspect of the present invention, a housing having a first end and a second end is provided. The first end of the housing has a bore for receiving a seat fixture. The housing further comprises an axial passage extending through the second end of the housing and into the bore. The seat fixture has a first end and a second end in an axial passage extending between the first and second ends. The first end of the seat fixture is supported within the bore of the housing at the first end thereof. The axial passage of the seat fixture is wider at the first end of the seat fixture for receiving a seat insert. The seat insert receives the head of the valve and the stem of the valve extends through the axial passages of the seat insert and housing and out the second end of the housing. The valve engages at least one actuator for applying force to the valve in a first axial direction to simulate a lifting of the valve off of the seat insert and in a second opposite axial direction to simulate a rapid movement of the valve head downward onto the seat insert. The valve also engages a motor which rotates the valve during the cyclic seating and unseating operation. By permitting rotation of the valve during the cyclic seating and unseating, the apparatus can more accurately simulate actual operating conditions.
In another aspect of the present invention, a testing apparatus has a housing having a first end and a second end. The first end of the housing has a bore for receiving a seat fixture. The housing also comprises an axial passage extending through the second end of the housing and into the bore. The seat fixture has a first end, a second end and an axial passage extending therebetween. The first end of the seat fixture is supported within the bore of the housing and at the first end of the housing. The axial passage of the seat fixture is wider at the first end of the seat fixture where a seat insert is received. The seat insert, in turn, receives the head of the valve and the stem of the valve extends through the axial passages of both the seat fixture and the housing and out the second end of the housing. The valve is engaged by at least one actuator that applies force to the valve in a first axial direction which lifts the head or moves the head laterally off of the valve seat. The actuator also moves the valve in a second opposite direction where the head is moved into engagement with the valve seat. A motor engages the valve and rotates the valve during the cyclic seating and unseating operation. The apparatus also includes a heater for heating the valve and associated components to simulate actual operating conditions. The bore of the housing and the seat fixture define an annular gap for accommodating coolant flow for cooling the valve after the heater heats the valve to simulate a hot/cold operating condition. The coolant flow is provided by a pressurized coolant supply that passes through a variable restrictor prior to passing through the annular gap. The testing apparatus also has at least one temperature probe for measuring the temperature of the valve. The testing apparatus includes a controller linked to the actuator, motor, heater, variable resistor and temperature probe for controlling the forces applied to the valve by the actuator, the rotation imparted to the valve by the motor, the heat applied to the valve by the heater and the coolant applied to the annular gap to render an automated apparatus.
In yet another aspect of the present invention, a method for testing engine valves is disclosed. The method includes providing an apparatus having a housing having a first end and a second end. The first end of the housing has a bore for receiving a seat fixture. The housing further has an axial passage extending through the second end of the housing and into the bore. The seat fixture has a first end, a second end and an axial passage extending therebetween. The first end of the seat fixture is supported within the bore of the housing at the first end of the housing. The axial passage of the seat fixture is wider at the first end of the seat fixture where it receives a seat insert. At least one actuator is provided for applying forces to the valve in opposite axial directions. The method further includes inserting a valve into the apparatus so the head of the valve is received in the seat insert and the stem of the valve extends through the passages of the seat fixture and the housing and out the second end of the housing so that the stem of the valve and the head of the valve engage the actuator. The method further includes operating the actuator in a repeating oscillating manner so that the valve head is repeatedly lifted off of the seat insert and pressed onto the seat insert. The method further includes rotating the valve while operating the actuator. The method further includes heating the valve with a heater to a first operating temperature range while operating the at least one actuator and while rotating the valve. The method also includes cooling the valve with at least one coolant to a second operating temperature range while operating the actuator and rotating the valve.